Field of Invention
The present invention relates to a Micro-Electro-Mechanical System (MEMS) acoustic pressure sensor device and its manufacturing method, in particular to such device that includes a multilayer structure having multiple metal sections, wherein the multiple metal sections of one metal layer and those of at least another metal layer are staggered, and a method for making such device.
Description of Related Art
FIG. 1 shows a multilayer MEMS structure disclosed in U.S. Pat. No. 7,202,101. As shown in FIG. 1, the multilayer MEMS structure 10 is formed on a substrate 11 and it includes: a sacrificial layer 12 formed on the substrate 11; a fixed electrode 13; a sacrificial layer 14; a first metal layer 15 formed on the sacrificial layer 14; a sacrificial layer 16; a second metal layer 17 formed on the sacrificial layer 16; a sacrificial layer 18; and a flexible or movable diaphragm 19 formed by sealing each metal layer with a polymer film.
In this prior art, the first metal layer 15 is a mesh-shaped metal layer to improve the properties of the MEMS acoustic pressure sensor device, wherein the mesh metal layer allows etching vapor to pass through the metal layers so that the etching vapor can react with and remove the desired portions of the sacrificial layers 12, 14, 16 and 18. In addition, the mesh metal layer 15 also alleviates the stress issue of the multilayer MEMS structure.
However, this mesh metal layer decreases the sensitivity of acoustic pressure and restricts the applications of the MEMS device. To counter, a part of the sacrificial layers 12, 14, 16 and 18 is removed, and a polymer material is deposited around each mesh metal layer for sealing each mesh metal layer so that the sensitivity can be enhanced thereby. Nevertheless, this polymer deposition process is not commonly available in a CMOS manufacturing fab, and it is difficult to integrate the polymer deposition process with the current CMOS manufacturing process.
For reference, U.S. Pat. No. 6,622,368, No. 7,049,051, No. 7,190,038 and No. 6,936,524 disclose other related MEMS acoustic pressure sensor devices.
In the view of above, to overcome the drawback in the prior art, the present invention proposes a multilayer structure with staggered metal layers and its manufacturing method.